Paper:	VLA HI Zeeman Observations toward W49A
Volume:	267, Hot Star Workshop III: the Earliest Stages of Massive Star Birth
Page:	349
Authors:	Brogan, C. L.; Troland, T. H.
Abstract:	We report VLA HI Zeeman observations toward the W49A star-forming region and the SNR W49B. Line of sight magnetic fields Blos of 60 to 300 mu G at 25 arcsec resolution were detected toward W49A at velocities of 4km/s and 7km/s. The Blos values measured toward W49A show a significant increase in field strength with higher resolution especially for the 4km/s HI component. In general, the HI gas in the velocity range -5 to 25 km/s toward W49A shows good agreement both kinematically and spatially with molecular emission known to be intrinsically associated with W49A. We estimate that the W49A North core is significantly subvirial (2T/W approx 0.2), and that the total kinetic + magnetic energies amount to less than 1/3 of the total W49A North gravitational energy. These magnetic field results suggest that W49A North is unstable to overall gravitational collapse in agreement with evidence that the halo is collapsing onto the W49A North ring of HII regions.

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